Electric unloader for air-compressors.



No. 792,787. PATENTED JUNE 20, 1905. W. PRBLLWITZ. ELECTRIC UNLOADER FOR AIR GOMPIRBSSORS.

APYLIGATION FILED Nov.2o,19os.

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RECEIVER w f7 K VALVE CAP [ll/AUST No. 792,787. PATENTED JUNE 20, 1905.

W. PRELLWITZ.

ELECTRIC UNLOADBR FOR AIR COMPRESSORS.

APPLICATION FILED Nov.2o,19oa.

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( afer/rfa No. 792,787. PATENTED JUNE 20, 1905.

W. PRELLWITZ. ELECTRIC UNLOADER POR AIR COMPRESSORS.

APPLICATION FILED NOV.20, 1903.

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Millesses.- [III/enfan- JJhM/#yf M UNITED STATES Patented June 2, 1905.

PATENT OFFICE.

VILLIAM PRELLVITZ, OE EASTON, PENNSYLVANIA, ASSIGNOR TO THE INGERSOLL-SERGEANT DRILL COMPANY, OF NEW YORK, N. Y., A CORPORATION OF WV EST VIRGINIA.

ELECTRIC UNLOADER FOR AIR-COMPRESSORS.

SPECIFICATION forming part of Letters Patent No. 792,787, dated June 20, 1905.

Application filed November 20, 1903. Serial No. 181.996.

To a/ZZ 'La7/1,0mJ it may concern.-

Be it known that I, IVILLIAM PaELLwI'rZ, a citizen of the United States, and a resident of Easton, in the county of Northampton and State of Pennsylvania, have invented a new and useful Electric Unloader Afor Air-Compressors, of which the following is a specilication.

This invention consists in an electric unloader 'for air-compressors, and relates particularly to an automatic magnetic unloader used in connection with the automatic starting and stopping of an electric-driven air-compressor.

The object of this invention is to provide a device of the above character which may be used to unload the air-compressor before starting, so that the inrush current necessary for starting the compressor shall be reduced to as small an amount as possible for practical operation.

A further object is to provide a device of the above character in which the load is thrown on when the motor and compressor reach a predetermined speed, the point being' determined by the connection of the unloader with the rheostat resistance, so that the unloader will be cut out at the point desired by the rheostat-arm.

A practical embodiment of this invention is represented in the accompanying' drawings, in which-w Eigure l represents the electric unloader in 'front elevation, the main valve and its adjacent parts being shown in section. Eig. Qis a transverse vertical section through the unloader and valve, the parts being' in the position which they assume when the current is olf the unloader-magnet. Eig. 3 is a detail cross-section taken in the plane of the line A of Eig. 2 looking' in the direction of the arrow. Fig. 3" is a similar view taken in the plane of the line B. Fig. 4 is a diagrammatic'view showing the relative positions ofthe unloader, the automatic starting and stopping devices, and the wiring therefor. Eig. 5 is a diagrammatic view showing the relation of the unloader to the rheostat and the wiring of a manually-operated device, and Fig. 6 is a detail sectional view of one of the valve-caps.

The main valve of the air-compressor regulator, which controls the opening and closing of the spaces back of the discharge-valves to the atmosphere, is denoted by 1, its piston by 2, and its box by 3. The auxiliary slide-valve is denoted by 4 and is located in a box 5 at one side of the valve-box 3. The supply-port to the auxiliary valve-box 5 is denoted by This auxiliary valve I controls the movement of thc main valve l as follows: Then the auxiliary slide-valve is at the limit of its downward movement, it will admit pressure to the proper side of the piston 2 of the main valve l to cause it to move the main valve into position to open communication from the intercooler to the back of the low-pressure valvecap of the compressor. Then the auxiliary slide-valve 4 is raised tothe limit of its upward movement, it will admit pressure to the other side of the piston 2 of the main valve l, thus sliding the main valve into position to open the backs of the high-pressure valve-cap and low-pressure valve-cap to the exhaust or atmosphere.

The unloadercasing (denoted by 6) surmounts the valve-box 5. This casing 6 has located therein an electromagnet 7 of the solenoid type. The armature of the electromagnet 7 (denoted by 8) is provided with a bar 9, depending therefrom, which bar is connected to and fitted to operate the auxiliary slidevalve 4:. The lower end of the bar 9 extends through the bottom of the valve-box 5 and is inclosed by afhollow cap 10.

A collar l1 is adjustably secured upon the lower end of the bar 9 by nuts 12, between which collar and the bottom of the valve-box 5 is interposed a spring 13, serving to normally hold the bar 9, and thereby the auxiliary valve 4, at the limit of its downward movement.

The electromag'net 7 of the unloader is automatically energized and deenergized for operating the auxiliary valve et, and thereby controlling the movements of the main valve 1, by the 'following devices: The air-pressurevIO governed electric contactor is denoted by 14 and is provided with the usual contacts 15 and 16 and linger 17. The motoris denoted by 18. The magnetic clutch is denoted as a whole by 19 and is positively driven from any suitable source-Mas, for instance, the motor, through connections not shown herein-by a shaft 20 and worm-and-gear connection 21 22. The coil of the magnetic clutch 19 is denoted by 26, which coil when energized serves to operate a link 27, connected to the arm 28 of the rheostat 29. The holding-magnet for the arm 28 of the rheostat is denoted by 30. The magnetic-controlled contactor is denoted by 31, and it is provided with coils 32 33, adaptedl to be short-circuited by the air-pressure-governed electric contactor 14. When both coils 32 33 are energized, the core will not be moved, but will remain in either extreme position, depending upon which coil was energized last. The magnetic switch is denoted by 34 and its controlling-coil by 35. The

main-line switch is denoted by 36, and the line wires leading therethrough by 37 38. The coil of an electric blow-out magnet for preventing sparking in the magnetic switch 34 is denoted by 47. Resistances 48 49 are located between the negative side of the main circuit at the magnetic clutch 19 and the coils 32 33, respectively, of the magnetic-controlled contactor 31. A resistance 50 is also shown between the magnetic-switch-controlling coil 35 and the holding-magnet 30.

The operation of the unloader is as follows: Let it be assumed that the air-compressor has stopped at a predetermined high pressure. As the air-pressure in the receiver falls the air-pressure-governed electric contacto'r 14 will cause the finger 17 to make connection with the contact 15. This will short-circuit the coil 33 in the magnetic contactor 31, because of greater resistance in the coil 33 over a connection through point 15, allowing the core 39 to be drawn up into engagement with .contact 40 by the coil 32, thus making circuit through the electric controlling-coil 35, magnetic clutch-coil 26, and holding-magnet 30. Immediately upon the contact being made in the electric contactor 31 the main circuit will be thrown in by the magnetic switch 34 at the point 37. As soon as this main contact is made at 37 the current is thrown onto the motor through the rheostat 29, and consequently through the electromagnet 7 of the unloader, which electromagnet is part of the rheostat resistance. Immediately upon current being passed through the electromagnet 7 the armature 8, and thereby the bar 9, is raised, thus moving the auxiliary valve 4 into position to cause the main valve to be operated to open the spaces back of the high and low pressure valve-caps to the atmosphere, and thus unload the compressor. Suficient current is provided through the first point of resistance in the rheostat to allow the motor 18 to start. Upon the starting of the motor, and thereby the compressor, the magnetic clutch 19 is operated, it being mechanically driven from the motor 18. The operation of the magnetic clutch will lift the link 27, and therebyswing the arm 28 of the rheostat over the resistance-coils, thus cutting out the resistance in the rheostat and causing the motor and compressor to gain speed. The arm 28 of the rheostat will be drawn into contact with the holding-magnet 30, thus cutting out all of the resistance of the rheostat. As soon as the rheostat-arm 28 comes in contact with the holding-magnet 30 the magnetic clutch-coil 26 is denergiz'ed, because less resistance is presented th rough the arm 28 to the opposite pole of the circuit than through the magnetic clutch-coil. This'denergization of the clutch-coil 26 will release the link 27 and permit the arm 28 of the rheostat to drop as soon as the circuit is broken through the holding-magnet 30. The electromagnet 7 of the unloader is connected in series with the rheostat resistance at some point. In the present instance it is shown at the last point of resistance, so that when the arm 28 reaches this point the electromagnet 7 of the unloader is cut out. As soon as the electromagnet 7 is cut out the armature and its bar 9 are caused to return to their normal position, thus again moving the auxiliary valve 4 into position to cause the main valve 1 to load the compressor. In the present instance the relation of the parts is such that the motor and compressor may reach practically full speed before the load is thrown onto the compressor. After the load has been thrown onto the compressor andthe air-pressure in the receiver rises to apredetermined high-pressure point the finger 17 ofthe air-pressure-governed electric contacter will make contact with the point 16, thus short-circuiting the coil 32 in the electric `contactor 31, thereby allowing the same to break the circuit through the starting device. This immediately releases the magnetic switch 34 and breaks the main circuit through the motor at the point 41, thereby releasing the entire apparatus. The current through the holdingmagnet 30 is also broken by the breaking of the circuit between the core 39 and contact 40, thus permitting the arm 28 of the rheostat to fall to its normal position. The compressor will remain loaded until the apparatus is again started, as above described.

In Fig. 5 I have shown a diagrammatic view illustrating a hand starting device in combination with the unloader for the compressor. In this instance when the main switch 36 is closed a circuit will be established through the rheostat 29, and thereby through the electromagnet of the unloader. As the arm 28 of the rheostat is moved by hand to cut out the resistance-coils in the rheostat the motor 18 will be started, and as the arm 28 reaches the holding-magnet 30 the motor, and thereby the IOO IIO

compressor, will have attained full speed and the unloader-eleetromagnet Will be cut out.

That I claim is l. An air -compressor, a discharge-valve therefor, a main regulator-valve for controlling' the pressure behind the discharge-valve, an auxiliary valve for controlling the movements of the main regulator-valve and electrical means for controlling the movements of the auxiliary valve.

2. An air-compressor, a dischargevalve therefor, a main regulator-valve for controlling the pressure behind the discharge-valve, an auxiliary valve Afor controlling the movements of the main regulator-valve and an electromagnet 'for operating the auxiliary valve.

3. A compound air-compressor, high and low pressure discharge-valves therefor, a main regulator-valve for controlling the pressure behind the high and low pressure dischargeence of two witnesses, this 12th 4day of October, 1908.

IVILLIA M PRELLVITZ. l/Vitnesses:

WARD RAYMOND, GEORGE HARTMANN. 

